One of the most complex problems facing test system design today is the need to provide system functions to each point of an electrical device or circuit under test. Common methods of doing this utilize switching systems to select a certain type of test function for each point to be tested. This switching is complex and expensive, and also generally is both physically large and consumes high levels of power. The circuitry of the switch also induces other problems and inaccuracies into the test circuit. The resistance or reactance of the switches, along with the separation of the device under test from the test equipment, all contribute this.
In the testing of large volumes of a single product it is common to find test systems designed and dedicated to this single function. If more flexibility is desired, it is sometimes possible to build a system up of standard units needing only a special interface, cable and so forth for a specific device to be tested. Beyond these application there is a wide range of what may be considered to be "universal" testers. These are customized to the testing of a specific part, not primarily by changing hardware although this is sometimes done and test heads are commonly changed, but by the changing of configuration through software.
The most common type of test system is commonly referred to as a "shared resource" design. This design uses a limited number of pieces of standard test equipment that is switched between many points of test connection by a switch matrix commonly known as a "cross-point switch". While these designs provide great flexibility in the application of proven standard test equipment, they suffer several serious limitations. The switch unit, if capable of high frequencies and high power levels in particular, is large, complex, and expensive. Its effect on the paths within the circuit may sometimes make the data collected invalid.
To solve these problems in the testing of complex, high speed parts, such as VLSI integrated circuits, some users have gone to a "tester per pin" design. This methodology duplicates all needed test equipment for each point to be tested. It can readily be seen that this design, while powerful, is priced out of all but the most demanding applications.